Tennessee Wastewater Operator Practice Exam

When is the best time to return supernatant from a digester?

1. During high flow periods

2. During maintenance shutdowns

3. During periods of low flow

4. During peak operational hours

The correct answer is: During periods of low flow

Returning supernatant from a digester during periods of low flow is ideal for several reasons. First, during low flow conditions, the overall demand on the treatment system is reduced, which allows for better management and stabilization of the process. This reduces the risks of overloading the system or causing disturbances in treatment efficiency. Moreover, during low-flow periods, there is typically less dilution in the downstream processes. This means that the return of supernatant, which is generally nutrient-rich and may contain higher levels of suspended solids, can be more effectively integrated into the treatment system without overwhelming it. By introducing this supernatant when flows are low, operators can ensure that the treatment system can adequately handle the return, allowing for optimal biological activity and enhanced digestion processes. In contrast, returning supernatant during high-flow periods or peak operational hours could lead to system strain, which may result in inadequate treatment and potential permit violations. Similarly, conducting this activity during maintenance shutdowns is impractical as the system is not fully operational and may not properly process the supernatant being returned.